28 o 
L ang. — The Prothallus 
are known, associated with differences in the young sporophyte. 
The possible systematic importance of these characters of the 
gametophyte in determining the relationship of the species of 
Lycopodium to one another has been pointed out by Dr. Treub, 
to whose investigations our entire knowledge of the life-history 
of tropical species is due ; the subject will be further discussed 
below. 
The present paper deals with the prothallus of Lycopodium 
clavatum , a preliminary account 1 of which was read before 
Section K of the British Association last year. During some 
weeks spent at Clova in Forfarshire, where all the British 
species of Lycopodium, with the exception of L. inundatum , 
can be found in abundance, the soil in which the plants grew 
was repeatedly examined in the hope of finding prothalli, 
but without success. In July of last year, however, a 
number of young plants of L. clavatum were found growing 
among a patch of Racomitrium lanuginosum on a rock shaded 
by a few trees in Glen Doll. Since the presence of the ‘ foot 5 
rendered it certain that these plants had been borne on 
prothalli, the thin layer of peaty soil underlying the moss was 
examined with great care, every part of it being gently 
crumbled down. In this way seven prothalli were found, 
three of which bore young plants of various ages. Careful 
examination of the ground for a considerable distance around 
failed to disclose any more young plants, nor were old plants 
of this species to be found near the spot. 
External Form and Structure of the Prothallus. 
The size and general appearance of the prothalli and young 
plants, upon the study of which the following description is 
founded, will be evident from Fig. 1, which is reproduced from 
a natural-size photograph of a prothallus seen from above, 
and of one of the smaller plants ; the foot of the latter is still 
recognizable though the prothallus to which it had been 
attached had disappeared. Although the material did not 
1 British Association Report, 1898, p. 1050. 
